Fatigue damage evolution in ZrO2-reinforced Al7075 metal matrix composites: from S-N curves to Paris multilinear regimes

Aluminum Matrix Composites (AMCs) are increasingly used in aerospace, automotive and marine applications, where structural components are often subjected to cyclic and time-varying loading conditions. A reliable assessment of their fatigue response is therefore essential for safe design and damage-tolerant applications. In this study, the fatigue behaviour of an Al7075 alloy reinforced with 1.5 wt% zirconium dioxide nanoparticles (ZrO2) is experimentally investigated, with particular attention to both fatigue lifetime and crack propagation response. The experimental programme first includes monotonic tensile tests, aimed at determining the static mechanical properties of the investigated nano-reinforced AMC and defining suitable load levels for subsequent cyclic tests. Fatigue life tests are then carried out under cyclic tensile loading at a stress ratio of 0.10, while fatigue crack propagation tests are performed at different stress ratios, namely 0.10, 0.50 and 0.75. To support the mechanical interpretation of the results, fracture surfaces are examined through optical macrographs and high-resolution scanning electron microscopy, allowing the main crack propagation and failure mechanisms to be identified. The experimental findings are compared with literature data available for both unreinforced aluminum alloys and ZrO2-reinforced AMC. The main novelty of the study lies in the integrated analysis of fatigue life, crack propagation behaviour and fractographic evidence within the same experimental framework. To the best of the authors’ knowledge, such a comprehensive investigation has not yet been reported in the literature for the composite system examined herein. While previous investigations often considered S-N fatigue response and fatigue crack propagation separately, the present work bridges these two aspects, providing a more complete description of damage evolution in ZrO2-reinforced Al7075 AMCs. This integrated dataset offers useful experimental support for the calibration and validation of fatigue damage models for nano-reinforced AMCs operating under service-like cyclic loading conditions.